Techniques for programmable beam steering compensation in scanning lidar systems

ABSTRACT

A system including an optical scanner to transmit an optical beam towards an object. The system includes a first optical element to receive a returned reflection having a lag angle; and direct the returned reflection to generate a first directed beam. The system includes a beam directing unit to receive the first directed beam; and direct, based on a first array voltage, the first directed beam to generate a second directed beam at a first location on a different optical element. The beam directing unit to direct, based on a second array voltage, the second steered beam from the first location on the different optical element to a second location on the different optical element to compensate for the lag angle.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/859,956, entitled “TECHNIQUES FOR PROGRAMMABLE BEAM STEERINGCOMPENSATION IN SCANNING LIDAR SYSTEMS,” filed on Jul. 7, 2022, thedisclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to optical detection, and moreparticularly to systems and methods for programmable beam steeringcompensation in a scanning light detection and ranging (LIDAR) system toenhance detection of distant objects.

BACKGROUND

A LIDAR system includes an optical scanner to transmit afrequency-modulated continuous wave (FMCW) infrared (IR) optical beamand to receive a return signal from reflections of the optical beam; anoptical processing system coupled with the optical scanner to generate abaseband signal in the time domain from the return signal, where thebaseband signal includes frequencies corresponding to LIDAR targetranges; and a signal processing system coupled with the opticalprocessing system to measure energy of the baseband signal in thefrequency domain, to compare the energy to an estimate of LIDAR systemnoise, and to determine a likelihood that a signal peak in the frequencydomain indicates a detected target.

SUMMARY

One aspect disclosed herein is directed to a method includingtransmitting, by an optical scanner, an optical beam towards an objectbased on a transmit optical beam that propagates along an optical axis.The method includes receiving, by a first optical element responsive tothe transmit of the optical beam, a returned reflection having a lagangle relative to the optical axis. The method includes steering, by thefirst optical element, the returned reflection to generate a firststeered beam. The method includes receiving, by a beam steering unit,the first steered beam and a local oscillator (LO) signal associatedwith the transmit optical beam, wherein the first steered beam ispropagating at a first beam angle relative to the optical axis and theLO signal is propagating at a first LO angle relative to the opticalaxis. The method includes steering, by the beam steering unit, the firststeered beam based on an array voltage to generate a second steered beamat a first location on a photodetector. The method includes steering, bythe beam steering unit, the LO signal based on the array voltage togenerate a steered LO signal at a second location on the photodetector,wherein a beam offset between the first location and the second locationis caused by the lag angle. The method includes adjusting, by aprocessor, the array voltage to cause the beam steering unit to reducethe beam offset between the first location and the second location.

In another aspect, the present disclosure is directed to a systemincluding an optical scanner to transmit an optical beam towards anobject based on a transmit optical beam that propagates along an opticalaxis. The system includes a first optical element to receive, responsiveto the transmit of the optical beam, a returned reflection having a lagangle relative to the optical axis; and steer the returned reflection togenerate a first steered beam. The system includes a beam steering unitto receive the first steered beam and a local oscillator (LO) signalassociated with the transmit optical beam, wherein the first steeredbeam is propagating at a first beam angle relative to the optical axisand the LO signal is propagating at a first LO angle relative to theoptical axis. The beam steering unit is further to steer the firststeered beam based on an array voltage to generate a second steered beamat a first location on a photodetector. The beam steering unit isfurther to steer the LO signal based on the array voltage to generate asteered LO signal at a second location on the photodetector, wherein abeam offset between the first location and the second location is causedby the lag angle. The system includes a processor to adjust the arrayvoltage to cause the beam steering unit to reduce the beam offsetbetween the first location and the second location.

In another aspect, the present disclosure is directed to a systemincluding an optical scanner to transmit an optical beam towards anobject based on a transmit optical beam that propagates along an opticalaxis. The system includes a first optical element to receive, responsiveto the transmit of the optical beam, a returned reflection having a lagangle relative to the optical axis; and steer the returned reflection togenerate a first steered beam. The system includes a beam steering unitto receive the first steered beam, wherein the first steered beam ispropagating at a first beam angle relative to the optical axis. The beamsteering unit is further to steer, the first steered beam based on anarray voltage to generate a second steered beam at a first location on aphotodetector. The system includes a processor to adjust the arrayvoltage to cause the beam steering unit to steer the second steered beamfrom the first location on the photodetector to a second location on thephotodetector to compensate for the lag angle.

These and other features, aspects, and advantages of the presentdisclosure will be apparent from a reading of the following detaileddescription together with the accompanying figures, which are brieflydescribed below. The present disclosure includes any combination of two,three, four or more features or elements set forth in this disclosure,regardless of whether such features or elements are expressly combinedor otherwise recited in a specific example implementation describedherein. This disclosure is intended to be read holistically such thatany separable features or elements of the disclosure, in any of itsaspects and example implementations, should be viewed as combinableunless the context of the disclosure clearly dictates otherwise.

It will therefore be appreciated that this summary is provided merelyfor purposes of summarizing some example implementations so as toprovide a basic understanding of some aspects of the disclosure.Accordingly, it will be appreciated that the above described exampleimplementations are merely examples and should not be construed tonarrow the scope or spirit of the disclosure in any way. Other exampleimplementations, aspects, and advantages will become apparent from thefollowing detailed description taken in conjunction with theaccompanying figures which illustrate, by way of example, the principlesof some described example implementations.

BRIEF DESCRIPTION OF THE FIGURE(S)

Embodiments and implementations of the present disclosure will beunderstood more fully from the detailed description given below and fromthe accompanying drawings of various aspects and implementations of thedisclosure, which, however, should not be taken to limit the disclosureto the specific embodiments or implementations, but are for explanationand understanding only.

FIG. 1 is a block diagram illustrating an example of a LIDAR system,according to some embodiments;

FIG. 2 is a time-frequency diagram illustrating an example of an FMCWscanning signal that can be used by a LIDAR system to scan a targetenvironment, according to some embodiments;

FIG. 3 is a block diagram illustrating an example environment for usingan optical scanner to transmit optical beams towards distant objects andreceive returned optical beams having different lag angles, according tosome embodiments;

FIG. 4 is a block diagram illustrating an example environment for beamsteering compensation in the LIDAR system 100 in FIG. 1 to enhancedetection of distant objects, according to some embodiments;

FIG. 5 is a block diagram illustrating an example environment for beamsteering compensation in the LIDAR system 100 in FIG. 1 to enhancedetection of distant objects using an additional lens, according to someembodiments;

FIG. 6A is a block diagram illustrating an example beam steering unit,according to some embodiments;

FIG. 6B is a block diagram illustrating an example beam steering unit,according to some embodiments;

FIGS. 7A-7B are block diagrams illustrating an example equation thatmodels the performance of the beam steering unit 430 in FIG. 4 ,according to some embodiments;

FIG. 8 is a block diagram illustrating an example structure of a beamsteering unit, according to some embodiments;

FIG. 9 is a graph illustrating the relationship between control voltageand birefringence phase delay or retardation of a beam steering unit,according to some embodiments; and

FIG. 10 is a flow diagram illustrating an example method for beamsteering compensation in an FMCW LIDAR system to enhance detection ofdistant objects, according to some embodiments.

DETAILED DESCRIPTION

According to some embodiments, the described LIDAR system usingprogrammable beam steering compensation may be implemented in a varietyof sensing and detection applications, such as, but not limited to,automotive, communications, consumer electronics, and healthcaremarkets. According to some embodiments, the described LIDAR system usingprogrammable beam steering compensation may be implemented as part of afront-end of frequency modulated continuous-wave (FMCW) device thatassists with spatial awareness for automated driver assist systems, orself-driving vehicles. According to some embodiments, the disclosedconfiguration may be agnostic to specific optical scanning architectureand can be tailored to enhance scanning LIDAR performance for a desiredtarget range and/or to increase frame rate for a given range on the fly.

In a coherent LIDAR system, a frequency-modulated continuous wave (FMCW)transmitted light source (Tx) is used to determine the distance andvelocity of objects in the scene by mixing a copy of the Tx source,known as the local oscillator (LO), with the received light (Rx) fromthe scene. The LO and Rx paths are combined on a fast photodiode (e.g.,a photodetector), producing beat frequencies, proportional to objectdistance, which are processed electronically to reveal distance andvelocity information of objects in the scene. To generate a point-cloudimage, scanning optics are commonly used to deflect the Tx beam (e.g.,signal) through the system field of view (FOV), comprising azimuth andzenith angles. In many applications, it is desirable to simultaneouslyachieve the highest possible scan rate and a large signal-to-noise ratio(SNR), as these two parameters directly affect the frame-rate of theLIDAR system, its maximum range (e.g., distance), range and velocityresolution, and the lateral spatial resolution.

However, increasing the scan rate produces a larger lag angle betweenthe Rx light from a given object and the corresponding local oscillator(LO) that the LIDAR system uses to process the Rx light. This lag angleeffect creates a beam walk-off problem, where the Tx light returned fromdistant objects are offset from the LO, which limits the achievablescan/frame rate and maximum range of the LIDAR system. Furthermore, thedetection of objects at a large range produces large beat frequencies.Therefore, detecting distant objects with high fidelity requires the useof analog-to-digital convertors (ADCs) with very large sampling rates,approaching Giga-samples per second (Gsps), which consume a large amountof power.

Accordingly, the present disclosure addresses the above-noted and otherdeficiencies by disclosing systems and methods for using beam steeringcompensation in a frequency-modulated continuous wave (FMCW) LIDARsystem to enhance detection of distant objects. As described in thebelow passages with respect to one or more embodiments, a LIDAR systemincludes an optical scanner to transmit an optical beam towards anobject based on a transmit optical beam that propagates along an opticalaxis. The LIDAR system includes a first optical element to receive,responsive to the transmit of the optical beam, a returned reflectionhaving a lag angle relative to the optical axis; and steer the returnedreflection to generate a first steered beam. The LIDAR system includes abeam steering unit to receive the first steered beam and a localoscillator (LO) signal associated with the transmit optical beam,wherein the first steered beam is propagating at a first beam anglerelative to the optical axis and the LO signal is propagating at a firstLO angle relative to the optical axis. The beam steering unit is furtherto steer the first steered beam based on an array voltage to generate asecond steered beam at a first location on a photodetector. The beamsteering unit is further to steer the LO signal based on the arrayvoltage to generate a steered LO signal at a second location on thephotodetector, wherein a beam offset between the first location and thesecond location is caused by the lag angle. The LIDAR system includes aprocessor to adjust the array voltage to cause the beam steering unit toreduce the beam offset between the first location and the secondlocation.

FIG. 1 is a block diagram illustrating an example of a LIDAR system,according to some embodiments. The LIDAR system 100 includes one or moreof each of a number of components, but may include fewer or additionalcomponents than shown in FIG. 1 . One or more of the components depictedin FIG. 1 can be implemented on a photonics chip, according to someembodiments. The optical circuits 101 may include a combination ofactive optical components and passive optical components. Active opticalcomponents may generate, amplify, and/or detect optical signals and thelike. In some examples, the active optical component includes opticalbeams at different wavelengths, and includes one or more opticalamplifiers, one or more optical detectors, or the like. In someembodiments, one or more LIDAR systems 100 may be mounted onto any area(e.g., front, back, side, top, bottom, and/or underneath) of a vehicleto facilitate the detection of an object in any free space relative tothe vehicle. In some embodiments, the vehicle may include a steeringsystem and a braking system, each of which may work in combination withone or more LIDAR systems 100 according to any information (e.g.,distance/ranging information, Doppler information, etc.) acquired and/oravailable to the LIDAR system 100. In some embodiments, the vehicle mayinclude a vehicle controller that includes the one or more componentsand/or processors of the LIDAR system 100.

Free space optics 115 may include one or more optical waveguides tocarry optical signals, and route and manipulate optical signals toappropriate input/output ports of the active optical circuit. Inembodiments, the one or more optical waveguides may include one or moregraded index waveguides, as will be described in additional detail belowat FIGS. 3-6 . The free space optics 115 may also include one or moreoptical components such as taps, wavelength division multiplexers (WDM),splitters/combiners, polarization beam splitters (PBS), collimators,couplers or the like. In some examples, the free space optics 115 mayinclude components to transform the polarization state and directreceived polarized light to optical detectors using a PBS, for example.The free space optics 115 may further include a diffractive element todeflect optical beams having different frequencies at different anglesalong an axis (e.g., a fast-axis).

In some examples, the LIDAR system 100 includes an optical scanner 102that includes one or more scanning mirrors that are rotatable along anaxis (e.g., a slow-axis) that is orthogonal or substantially orthogonalto the fast-axis of the diffractive element to steer optical signals toscan an environment according to a scanning pattern. For instance, thescanning mirrors may be rotatable by one or more galvanometers. Objectsin the target environment may scatter an incident light into a returnoptical beam or a target return signal. The optical scanner 102 alsocollects the return optical beam or the target return signal, which maybe returned to the passive optical circuit component of the opticalcircuits 101. For example, the return optical beam may be directed to anoptical detector by a polarization beam splitter. In addition to themirrors and galvanometers, the optical scanner 102 may includecomponents such as a quarter-wave plate, lens, anti-reflective coatedwindow or the like.

To control and support the optical circuits 101 and optical scanner 102,the LIDAR system 100 includes LIDAR control systems 110. The LIDARcontrol systems 110 may include a processing device for the LIDAR system100. In some examples, the processing device may be one or moregeneral-purpose processing devices such as a microprocessor, centralprocessing unit, or the like. More particularly, the processing devicemay be complex instruction set computing (CISC) microprocessor, reducedinstruction set computer (RISC) microprocessor, very long instructionword (VLIW) microprocessor, or processor implementing other instructionsets, or processors implementing a combination of instruction sets. Theprocessing device may also be one or more special-purpose processingdevices such as an application specific integrated circuit (ASIC), afield programmable gate array (FPGA), a digital signal processor (DSP),network processor, or the like.

In some examples, the LIDAR control system 110 may include a processingdevice that may be implemented with a DSP, such as signal processingunit 112. The LIDAR control systems 110 are configured to output digitalcontrol signals to control optical drivers 103. In some examples, thedigital control signals may be converted to analog signals throughsignal conversion unit 106. For example, the signal conversion unit 106may include a digital-to-analog converter. The optical drivers 103 maythen provide drive signals to active optical components of opticalcircuits 101 to drive optical sources such as lasers and amplifiers. Insome examples, several optical drivers 103 and signal conversion units106 may be provided to drive multiple optical sources.

The LIDAR control systems 110 are also configured to output digitalcontrol signals for the optical scanner 102. A motion control system 105may control the galvanometers of the optical scanner 102 based oncontrol signals received from the LIDAR control systems 110. Forexample, a digital-to-analog converter may convert coordinate routinginformation from the LIDAR control systems 110 to signals interpretableby the galvanometers in the optical scanner 102. In some examples, amotion control system 105 may also return information to the LIDARcontrol systems 110 about the position or operation of components of theoptical scanner 102. For example, an analog-to-digital converter may inturn convert information about the galvanometers' position to a signalinterpretable by the LIDAR control systems 110.

The LIDAR control systems 110 are further configured to analyze incomingdigital signals. In this regard, the LIDAR system 100 includes opticalreceivers 104 to measure one or more beams received by optical circuits101. For example, a reference beam receiver may measure the amplitude ofa reference beam from the active optical component, and ananalog-to-digital converter converts signals from the reference receiverto signals interpretable by the LIDAR control systems 110. Targetreceivers measure the optical signal that carries information about therange and velocity of a target in the form of a beat frequency,modulated optical signal. The reflected beam may be mixed with a secondsignal from a local oscillator. The optical receivers 104 may include ahigh-speed analog-to-digital converter to convert signals from thetarget receiver to signals interpretable by the LIDAR control systems110. In some examples, the signals from the optical receivers 104 may besubject to signal conditioning by signal conditioning unit 107 prior toreceipt by the LIDAR control systems 110. For example, the signals fromthe optical receivers 104 may be provided to an operational amplifierfor amplification of the received signals and the amplified signals maybe provided to the LIDAR control systems 110.

In some applications, the LIDAR system 100 may additionally include oneor more imaging devices 108 configured to capture images of theenvironment, a global positioning system 109 configured to provide ageographic location of the system, or other sensor inputs. The LIDARsystem 100 may also include an image processing system 114. The imageprocessing system 114 can be configured to receive the images andgeographic location, and send the images and location or informationrelated thereto to the LIDAR control systems 110 or other systemsconnected to the LIDAR system 100.

In operation according to some examples, the LIDAR system 100 isconfigured to use nondegenerate optical sources to simultaneouslymeasure range and velocity across two dimensions. This capability allowsfor real-time, long range measurements of range, velocity, azimuth, andelevation of the surrounding environment.

In some examples, the scanning process begins with the optical drivers103 and LIDAR control systems 110. The LIDAR control systems 110instruct, e.g., via signal processing unit 112, the optical drivers 103to independently modulate one or more optical beams, and these modulatedsignals propagate through the optical circuits 101 to the free spaceoptics 115. The free space optics 115 directs the light at the opticalscanner 102 that scans a target environment over a preprogrammed patterndefined by the motion control system 105. The optical circuits 101 mayalso include a polarization wave plate (PWP) to transform thepolarization of the light as it leaves the optical circuits 101. In someexamples, the polarization wave plate may be a quarter-wave plate or ahalf-wave plate. A portion of the polarized light may also be reflectedback to the optical circuits 101. For example, lensing or collimatingsystems used in LIDAR system 100 may have natural reflective propertiesor a reflective coating to reflect a portion of the light back to theoptical circuits 101.

Optical signals reflected back from an environment pass through theoptical circuits 101 to the optical receivers 104. Because thepolarization of the light has been transformed, it may be reflected by apolarization beam splitter along with the portion of polarized lightthat was reflected back to the optical circuits 101. In such scenarios,rather than returning to the same fiber or waveguide serving as anoptical source, the reflected signals can be reflected to separateoptical receivers 104. These signals interfere with one another andgenerate a combined signal. The combined signal can then be reflected tothe optical receivers 104. Also, each beam signal that returns from thetarget environment may produce a time-shifted waveform. The temporalphase difference between the two waveforms generates a beat frequencymeasured on the optical receivers 104 (e.g., photodetectors).

The analog signals from the optical receivers 104 are converted todigital signals by the signal conditioning unit 107. These digitalsignals are then sent to the LIDAR control systems 110. A signalprocessing unit 112 may then receive the digital signals to furtherprocess and interpret them. In some embodiments, the signal processingunit 112 also receives position data from the motion control system 105and galvanometers (not shown) as well as image data from the imageprocessing system 114. The signal processing unit 112 can then generate3D point cloud data (sometimes referred to as, “a LIDAR point cloud”)that includes information about range and/or velocity points in thetarget environment as the optical scanner 102 scans additional points.In some embodiments, a LIDAR point cloud may correspond to any othertype of ranging sensor that is capable of Doppler measurements, such asRadio Detection and Ranging (RADAR). The signal processing unit 112 canalso overlay 3D point cloud data with image data to determine velocityand/or distance of objects in the surrounding area. The signalprocessing unit 112 also processes the satellite-based navigationlocation data to provide data related to a specific global location.

FIG. 2 is a time-frequency diagram illustrating an example of an FMCWscanning signal that can be used by a LIDAR system to scan a targetenvironment, according to some embodiments. In one example, the scanningwaveform 201, labeled as f_(FM)(t), is a sawtooth waveform (sawtooth“chirp”) with a chirp bandwidth Δf_(C) and a chirp period T_(C). Theslope of the sawtooth is given as k=(Δf_(C)/T_(C)). FIG. 2 also depictstarget return signal 202 according to some embodiments. Target returnsignal 202, labeled as f_(FM)(t−Δt), is a time-delayed version of thescanning waveform 201, where Δt is the round trip time to and from atarget illuminated by scanning waveform 201. The round trip time isgiven as Δt=2R/v, where R is the target range and v is the velocity ofthe optical beam, which is the speed of light c. The target range, R,can therefore be calculated as R=c(Δt/2). When the return signal 202 isoptically mixed with the scanning signal, a range-dependent differencefrequency (“beat frequency”) Δf_(R)(t) is generated. The beat frequencyΔf_(R)(t) is linearly related to the time delay Δt by the slope of thesawtooth k. That is, Δf_(R)(t)=kΔt. Since the target range R isproportional to Δt, the target range R can be calculated asR=(c/2)(Δf_(R)(t)/k). That is, the range R is linearly related to thebeat frequency Δf_(R)(t). The beat frequency Δf_(R)(t) can be generated,for example, as an analog signal in optical receivers 104 of system 100.The beat frequency can then be digitized by an analog-to-digitalconverter (ADC), for example, in a signal conditioning unit such assignal conditioning unit 107 in LIDAR system 100. The digitized beatfrequency signal can then be digitally processed, for example, in asignal processing unit, such as signal processing unit 112 in system100. It should be noted that the target return signal 202 will, ingeneral, also includes a frequency offset (Doppler shift) if the targethas a velocity relative to the LIDAR system 100. The Doppler shift canbe determined separately, and used to correct (e.g., adjust, modify) thefrequency of the return signal, so the Doppler shift is not shown inFIG. 2 for simplicity and ease of explanation. For example, LIDAR system100 may correct the frequency of the return signal by removing (e.g.,subtracting, filtering) the Doppler shift from the frequency of thereturned signal to generate a corrected return signal. The LIDAR system100 may then use the corrected return signal to calculate a distanceand/or range between the LIDAR system 100 and the object. In someembodiments, the Doppler frequency shift of target return signal 202that is associated with an object may be indicative of a velocity and/ormovement direction of the object relative to the LIDAR system 100.

It should also be noted that the sampling frequency of the ADC willdetermine the highest beat frequency that can be processed by the systemwithout aliasing. In general, the highest frequency that can beprocessed is one-half of the sampling frequency (i.e., the “Nyquistlimit”). In one example, and without limitation, if the samplingfrequency of the ADC is 1 gigahertz, then the highest beat frequencythat can be processed without aliasing (Δf_(Rmax)) is 500 megahertz.This limit in turn determines the maximum range of the system asR_(max)=(c/2)(Δf_(Rmax)/k) which can be adjusted by changing the chirpslope k. In one example, while the data samples from the ADC may becontinuous, the subsequent digital processing described below may bepartitioned into “time segments” that can be associated with someperiodicity in the LIDAR system 100. In one example, and withoutlimitation, a time segment might correspond to a predetermined number ofchirp periods T, or a number of full rotations in azimuth by the opticalscanner.

FIG. 3 is a block diagram illustrating an example environment for usingan optical scanner to transmit optical beams towards distant objects andreceive returned optical beams having different lag angles, according tosome embodiments. The environment 300 includes the optical scanner 102(e.g., a prism, a mirror), an optical beam source 340, a collimationlens 320 (sometimes referred to as, “optical element”), and an opticaldevice 328 (sometimes referred to as, “optical element”). The opticaldevice 328 may be a lens, a glass plate (sometimes referred to as,“local oscillator window”), or a beam steering unit. In someembodiments, the glass plate may be reflection coated glass plate or apartially reflective glass plate.

In some embodiments, any of the components (e.g., optical scanner 102,optical beam source 340, collimation lens 320, optical device 328, etc.)in the environment 300 may be added as a component of the LIDAR system100 in FIG. 1 , or be used to replace or modify any of the one or morecomponents (e.g., free space optics 115, optical circuits, opticalreceivers 104, etc.) of the LIDAR system 100.

The environment 300 includes one or more objects, such as object 308 a(e.g., a street sign), object 308 b (e.g., a tree), and object 308 c(e.g., a pedestrian); each collectively referred to as objects 308.Although FIG. 3 shows only a select number of objects 308, theenvironment 300 may include any number of objects 308 of any type (e.g.,pedestrians, vehicles, street signs, raindrops, snow, street surface)that are within a short distance (e.g., 30 meters) or a long distance(e.g., 300 meters, 500 meters and beyond) from the optical scanner 102.In some embodiments, an object 308 may be stationary or moving withrespect to the optical scanner 102.

In some embodiments, the optical scanner 102 is configured to receiveone or more optical beams 304 (sometimes referred to as, “transmitoptical beam”) transmitted from the optical beam source 340 along anoptical axis 305 (shown in FIG. 3 as the X-axis). In some embodiments,the optical scanner 102 is configured to steer (e.g., redirect,transmit, scatter) the one or more optical beams 304 into free spacetoward the one or more objects 308, which causes the one or more opticalbeams to scatter into returned optical beams 306 a, 306 b, 306 c(collectively referred to as, “returned optical beams 306”). Forexample, the one or more optical beams 304 scatter against the object308 a to create a returned optical beam 306 a, which is returned to theLIDAR system 100. As another example, the one or more optical beams 304scatter against the object 308 b to create a returned optical beam 306b, which is returned to the LIDAR system 100. As another example, theone or more optical beams 304 scatter against the object 308 c to createa returned optical beam 306 c, which is returned to the LIDAR system100.

The collimation lens 320 is configured (e.g., positioned, arranged) tocollect (e.g., receive, acquire, aggregate) the returned optical beams306 that scatter from the one or more objects 308 in response to theoptical scanner 102 steering the one or more optical beams 304 into freespace. In some embodiments, the collimation lens 320 may be a symmetriclens having a diameter. In some embodiments, the collimation lens 320may be an asymmetric lens.

As shown in FIG. 3 , the lag angle between a respective returned opticalbeam 306 and the collimation lens 320 is indicated by θ_(DS,n), where nis an integer. For example, the lag angle between the returned opticalbeam 306 a and the collimation lens 320 is indicated by θ_(DS,0) (notshown in FIG. 3 ), the lag angle between the returned optical beam 306 band the collimation lens 320 is indicated by θ_(DS,1), and the lag anglebetween the returned optical beam 306 c and the collimation lens 320 isindicated by θ_(DS,2) (shown in FIG. 3 as, θ_(DS,n)). In someembodiments, increasing the scan rate of the optical scanner 102produces a larger lag angle between one or more of the returned opticalbeams 306.

As shown in FIG. 3 , the optical device 328 receives the returnedoptical beam 306 a at a location 1 (shown in FIG. 3 as, “L1”) on theoptical device 328 from the collimation lens 320 as a result of thereturned optical beam 306 a having a lag angle of zero degrees withrespect to the optical axis 305, and the collimation lens 320 generatinga collimated beam from the returned optical beams 306. The opticaldevice 328 also receives the returned optical beam 306 b at a location 2(shown in FIG. 3 as, “L2”) on the optical device 328 as a result of thereturned optical beam 306 b having a lag angle of θ_(DS,1) degrees withrespect to the optical axis 305, and the collimation lens 320 generatinga collimated beam from the returned optical beams 306. The opticaldevice 328 also receives the returned optical beam 306 c at a location 3(shown in FIG. 3 as, “L3”) on the optical device 328 as a result of thereturned optical beam 306 c having a lag angle of θ_(DS,2) degrees withrespect to the optical axis 305, and the collimation lens 320 generatinga collimated beam from the returned optical beams 306.

In other words, the respectively increasing lag angles of the returnedoptical beams 306 a, 306 b, 306 c from the distant objects cause theoptical device 328 to receive the returned optical beams 306 atdifferent locations on the optical device 328. The offset of a locationon the optical device 328 with respect to the optical axis 305 isreferred to as a beam walk-off (e.g., a distance). For example, thedifference in distance between location 2, where the optical device 328receives the returned optical beam 306 b, and location 1, where theoptical device 328 receives the returned optical beam 306 a, is referredto as beam walk-offs. The difference in distance between location 3,where the optical device 328 receives the returned optical beam 306 c,and location 2, where the optical device 328 receives the returnedoptical beam 306 b, is referred to as beam walk-off 2 (shown in FIG. 3as, “beam walk-off_(n)”).

Although not shown in FIG. 3 , the optical device 328 couples to theLIDAR control system 110 in FIG. 1 such to be able to pass any of thereturned optical beams that are received by the optical device 328 tothe LIDAR control system 110 for processing by the signal processingunit 112.

FIG. 4 is a block diagram illustrating an example environment for beamsteering compensation in the LIDAR system 100 in FIG. 1 to enhancedetection of distant objects, according to some embodiments. Theenvironment 400 includes the optical scanner 102, the collimation lens320 (sometimes referred to as, “lens 3”), and the optical beam source340. The environment 400 includes the optical device 328 from FIG. 3 ,but where the optical device 328 is a glass plate 428. In someembodiments, the glass plate 428 may be reflection coated glass plate ora partially reflective glass plate. The environment 400 includes a beamsteering unit 430, a lens 334 (sometimes referred to as, “lens 4”), anda photodetector 460. The environment 400 includes a voltage control unit120 that is communicatively coupled to the LIDAR control system 110. Insome embodiments, as shown in FIG. 1 , the voltage control unit 120 maybe a component of the LIDAR control system 110.

In some embodiments, any of the components (e.g., beam steering unit430, etc.) (e.g., optical scanner 102, optical beam source 340,collimation lens 320, glass plate 428, etc.) in the environment 400 maybe added as a component of the LIDAR system 100 in FIG. 1 , or be usedto replace or modify any of the one or more components (e.g., free spaceoptics 115, optical circuits, optical receivers 104, etc.) of the LIDARsystem 100.

The environment 400 includes an object 408, such as object 308 a in FIG.3 (e.g., a street sign), object 308 b in FIG. 3 (e.g., a tree), orobject 308 c in FIG. 3 (e.g., a pedestrian); each collectively referredto as objects 308. Although FIG. 4 shows only a single object 408, theenvironment 400 may include any number of objects 408 of any type thatare within a short distance (e.g., 30 meters) or a long distance (e.g.,300 meters, 500 meters and beyond) from the optical scanner 102. In someembodiments, an object 408 may be stationary or moving with respect tothe optical scanner 102.

An output terminal of the voltage control unit 120 is coupled to aninput terminal of the beam steering unit 430. The LIDAR control system110 may send instructions to the voltage control unit 120 to cause thevoltage control unit 120 to generate a control voltage (e.g., 5V) andprovide the voltage to the beam steering unit 430 via the outputterminal of the control voltage control unit 120. In some embodiments, aplurality of output terminals of the voltage control unit 120 may berespectively coupled to a plurality of input terminals of the beamsteering unit 430. As such, the LIDAR control system 110 may sendinstructions to the voltage control unit 120 to cause the voltagecontrol unit 120 to generate an array voltage (sometimes referred to as,“control voltages”) and provide the array voltage to the beam steeringunit 430 via the plurality of output terminal of the voltage controlunit 120. For example, the voltage control unit 120 may provide 4.5V toits first output terminal that is coupled to a first input terminal ofthe beam steering unit 430, the voltage control unit 120 may provide4.8V to its second output terminal that is coupled to a second inputterminal of the beam steering unit 430, the voltage control unit 120 mayprovide 0.0V to its third output terminal that is coupled to a thirdinput terminal of the beam steering unit 430, and so on.

The optical scanner 102 is configured to receive an optical beam 304transmitted from the optical beam source 340 along an optical axis 305(shown in FIG. 4 as the X-axis), where the optical beam 304 passesthrough the glass plate 428. Furthermore, the glass plate 428 reflects aportion of the optical beam 304 to generate a local oscillator (LO)signal 418 that propagates along the optical axis and toward location 2(shown in FIG. 4 as, “L2”) on the beam steering unit 430.

The optical scanner 102 is configured to steer the optical beam 304 intofree space toward the object 408, which causes the optical beam toscatter into returned optical beam 306 that is returned to the LIDARsystem 100.

The collimation lens 320 is configured to collect the returned opticalbeam 306. The scan rate of the optical scanner 102 and/or the distanceof the object 408 from the LIDAR system 100 causes the returned opticalbeam 306 to have a lag angle θ_(DS) with respect to the optical axis.

As shown in FIG. 4 , the glass plate 428 receives the returned opticalbeam 306 a at location 1 (shown in FIG. 3 as, “L1”) on glass plate 428as a result of the returned optical beam 306 a having a lag angle θ_(DS)is with respect to the optical axis 305, and the collimation lens 320generating a collimated beam from the returned optical beam 306. Theglass plate 428 steers the returned optical beam 306 to propagate alongthe optical axis and toward location 1 (shown in FIG. 4 as, “L1”) on thebeam steering unit 430.

Thus, the lag angle θ_(DS) is of the returned optical beam 306 a causesthe beam steering unit 430 to receive the returned optical beam 306 andthe local oscillator (LO) signal 418 at different locations (e.g., L1,L2) on the beam steering unit 430. This creates a beam walk-off (e.g.,an error) that is equal to the distance between L2 and L1. This beamwalk-off propagates to the LIDAR control system 110 and negativelyaffects the ability of the LIDAR control system 110 to accuratelycalculate metrics (e.g., distance, velocity, orientation, etc.) relatedto the object 408.

The beam steering unit 430, however, may be used to compensate (e.g.,mitigate or substantially eliminate) for the beam walk-off, which inturn, improves the processing capability of the LIDAR control system110. The beam steering unit 430 is an optical device that is transparentto the LIDAR laser wavelength (e.g., 905 nanometers (nm) and 1550 nm).The beam steering unit 430 may work in a transmissive or a reflectiveway to allow an optical beam (e.g., light) to pass thru it one or moretimes in reflection with a mirror. In one embodiment, the beam steeringunit 430 may be a thin liquid crystal filled plate with patternedelectrode to apply different voltage profiles on the liquid crystallayer to form a linear phase retardation along one direction. When theoptical beam passes thru the beam steering unit 430, it experiences alinear spatial phase on its wavefront (e.g., the set of all pointshaving the same phase change between adjacent points), which changes itsbeam direction depending on the linear phase direction in space.Depending on the angle change (lag angle) of the returned optical beams306 that is due at least in part to the scanning optics, the beamsteering unit 430 can be aligned with its linear phase direction in theangle shift direction of the returned optical beams 306. Thru itsprogrammable capability, the beam steering unit 430 can be configureddynamically to optimize the mixing performance thru tuning the angleoffset of the returned optical beams 306.

The LIDAR control system 110 may be configured to send instructions tothe voltage control unit 120 to cause the voltage control unit 120 togenerate one or more control voltages (e.g., a single voltage or avoltage array) and provide the one or more control voltages to the beamsteering unit 430 via the output terminal of the voltage control unit120. The one or more control voltages may, depending on the angle of thereturned optical beam 306 at L1 on the beam steering unit 430, cause thebeam steering unit 430 to change (e.g., adjust, modify) the angle of thereturned optical beam 306.

For example, the returned optical beam 306 at L1 may have a first anglewith respect to the optical axis 305. In response to receiving a controlvoltage V₁ from the voltage control unit 120, the beam steering unit 430may generate a returned optical beam 306 _(V1) that also has the samefirst angle. The beam steering unit 430 may provide the returned opticalbeam 306 _(V1) to the lens 334 such that the returned optical beam 306_(V1) propagates along the optical axis at the first angle and towardlocation 1 (shown in FIG. 4 as, “L1”) on the lens 334. Thus, the controlvoltage V₁ causes the beam steering unit 430 to allow the returnedoptical beam 306 to pass through the beam steering unit 430 withoutadjusting the first angle of the returned optical beam 306.

As another example, in response to receiving a control voltage V₂ fromthe voltage control unit 120, the beam steering unit 430 may generate areturned optical beam 306 _(V2) that has a second angle, where thesecond angle is different from the first angle. The beam steering unit430 may then provide the returned optical beam 306 _(V2) to the lens 334such that the returned optical beam 306 _(V2) propagates along theoptical axis at the second angle and toward location 2 (shown in FIG. 4as, “L2”) on the lens 334. Thus, the control voltage V₂ causes the beamsteering unit 430 to adjust the first angle of the returned optical beam306 to steer the returned optical beam 306.

As another example, in response to receiving a control voltage V₃ fromthe voltage control unit 120, the beam steering unit 430 may generate areturned optical beam 306 _(V2) that has the third angle, where thethird angle is different from both the first angle and the second angle.The beam steering unit 430 may then provide the returned optical beam306 _(V3) to the lens 334 such that the returned optical beam 306 _(V3)propagates along the optical axis 305 at the third angle and towardlocation 3 (shown in FIG. 4 as, “L3”) on the lens 334. Thus, the controlvoltage V₃ causes the beam steering unit 430 to adjust the first angleof the returned optical beam 306 to steer the returned optical beam 306.

The one or more control voltages may also, depending on its angle at L2on the beam steering unit 430, change the angle of the LO signal 418.For example, the LO signal 418 at L2 may have a first angle with respectto the optical axis 305. In response to receiving a control voltage V₁from the voltage control unit 120, the beam steering unit 430 maygenerate a LO signal 418 _(V1) that also has the same first angle. Thebeam steering unit 430 may provide the LO signal 418 _(V1) to the lens334 such that the LO signal 418 _(V1) propagates along the optical axisat the first angle and toward location 4 (shown in FIG. 4 as, “L4”) onthe lens 334. Thus, the control voltage V₁ causes the beam steering unit430 to allow the LO signal 418 to pass through the beam steering unit430 without adjusting the first angle of the LO signal 418.

As another example, in response to receiving a control voltage V₂ fromthe voltage control unit 120, the beam steering unit 430 may generate aLO signal 418 _(V2) that has second angle, where the second angle isdifferent from the first angle. The beam steering unit 430 may thenprovide the LO signal 418 _(V2) to the lens 334 such that the LO signal418 _(V2) propagates along the optical axis 305 at the second angle andtoward location 5 (shown in FIG. 4 as, “L5”) on the lens 334. Thus, thecontrol voltage V₂ causes the beam steering unit 430 to adjust the firstangle of the LO signal 418 to steer the LO signal 418.

As another example, in response to receiving a control voltage V₃ fromthe voltage control unit 120, the beam steering unit 430 may generate aLO signal 418 _(V2) that has the third angle, where the third angle isdifferent from both the first angle and the second angle. The beamsteering unit 430 may then provide the LO signal 418 _(V3) to the lens334 such that the LO signal 418 _(V3) propagates along the optical axis305 at the third angle and toward location 6 (shown in FIG. 4 as, “L6”)on the lens 334. Thus, the control voltage V₃ causes the beam steeringunit 430 to adjust the first angle of the LO signal 418 to steer the LOsignal 418.

The lens 334 is configured to receive one of the returned optical beams306 (e.g., returned optical beam 306 _(V1), returned optical beam 306_(V2), or returned optical beam 306 _(V3)) at its corresponding angle(e.g., first angle, second angle, or third angle) and steer the returnedoptical beam 306 (shown in FIG. 4 as, “returned optical beam 306 s”) topropagate along the optical axis toward location 1 (shown in FIG. 4 as,“L1”) on the photodetector 460. In some embodiments, depending on thelocation in which the beam steering unit 430 receives the returnedoptical beam 306, the lens 334 may either (a) steer the returned opticalbeam 306 by adjusting (e.g., adding or subtracting degrees) thecorresponding angle of the returned optical beam 306 to generate thereturned optical beam 306 s, or (b) allow the returned optical beam 306to pass through the lens 334 without adjusting the corresponding angleof the returned optical beam 306.

Similarly, the lens 334 is configured to receive one of the LO signal418 (e.g., LO signal 418 _(V1), LO signal 418 _(V2), or LO signal 418_(V3)) at its corresponding angle (e.g., first angle, second angle, orthird angle) and steer the LO signal 418 (shown in FIG. 4 as, “LO signal418 s”) to propagate along the optical axis 305 toward location 2 (shownin FIG. 4 as, “L2”) on the photodetector 460. In some embodiments,depending on the location in which the beam steering unit 430 receivesthe LO signal 418, the lens 334 may either (a) steer the LO signal 418by adjusting (e.g., adding or subtracting degrees) the correspondingangle of the LO signal 418 to generate the LO signal 418 s, or (b) allowthe LO signal 418 to pass through the lens 334 without adjusting thecorresponding angle of the LO signal 418.

Although, FIG. 4 shows that the beam steering unit 430 steers thereturned optical beams 306 and the LO signal 418 in the same downwarddirection (e.g., decreasing beam angle) relative to the optical axis305, the beam steering unit 430 may be configured to steer the returnedoptical beam 306 and the LO signal 418 in an upward direction. In someembodiments, the beam steering unit 430 may be configured to steer thereturned optical beam 306 and the LO signal 418 in opposite directions.For example, the beam steering unit 430 may be configured to steer thereturned optical beam 306 in an upward direction by adding degrees tothe angle of the returned optical beam 306, and steer the LO signal 418in a downward direction by subtracting degrees from the angle of the LOsignal 418; or vice versa. In some embodiments, the beam steering unit430 may be configured to adjust the angle of the returned optical beam306 and the LO signal 418 by an equal amount (e.g., 10 degrees, −10degrees, etc.).

The photodetector 460 receives the returned optical beam 306 (shown inFIG. 4 as, “returned optical beam 306 s”) at L1 and the LO signal 418(shown in FIG. 4 as, “LO signal 4185”) at L2. The distance between L1and L2 corresponds to a compensated beam walk-off because it is lessthan the beam walk-off at input (e.g., L1 and L2) of the beam steeringunit 430, and which was caused by the lag angle ° DS of the returnedoptical beam 306. The photodetector 460 can now more accurately detectthe returned optical beam 306 and the LO signal 418 at its inputs togenerate electrical signals having beat frequencies that are indicativeof the returned optical beam 306. The photodetector 460 then providesthe electrical signals to the LIDAR control system for processing tocalculate metrics (e.g., distance, velocity, orientation, etc.) relatedto the object 408.

Although not shown in FIG. 4 , the output of the photodetector 460couples to the LIDAR control system 110 in FIG. 1 such to be able topass any of its outputs (e.g., electrical signals) to the LIDAR controlsystem 110 for processing by the signal processing unit 112.

FIG. 5 is a block diagram illustrating an example environment for beamsteering compensation in the LIDAR system 100 in FIG. 1 to enhancedetection of distant objects using an additional lens, according to someembodiments. The environment 500 includes the same arrangement of thecomponents depicted in FIG. 4 , expect that the optical beam source 340is positioned between the beam steering unit 430 and the lens 324,instead of being positioned between the glass plate 428 and the beamsteering unit 430, as shown in FIG. 4 . In this alternate configuration,the optical beam source 340 is configured to transmit an optical beam304 along the optical axis 305 toward the beam steering unit 430. Thebeam steering unit 430 is configured to adjust, based the controlvoltage, an angle of the optical axis 305 to steer the optical axis 305.

The environment 500 also includes a lens 522 (sometimes referred to as,“L2”) positioned between the glass plate 428 and the beam steering unit430 to receive one or more optical beams (e.g., optical beam 304, LOsignal 418, returned optical beam 306). Depending on the location inwhich the beam steering unit 430 receives an optical beam, the lens 522may either (a) steer the optical beam by adjusting is angle, or (b)allow the optical beam to pass through the lens 522 without adjustingits angle.

FIG. 6A is a block diagram illustrating an example beam steering unit430, according to some embodiments. In this embodiment, the beamsteering unit 430 is a thin liquid crystal (LC) plate with a linearspatial phase that is configured (e.g., programmed) to steer or deflecta collimated beam.

FIG. 6B is a block diagram illustrating an example beam steering unit430, according to some embodiments. In this embodiment, the beamsteering unit 430 is a thin prism that is configured to steer or deflecta collimated beam.

FIGS. 7A-7B are block diagrams illustrating an example equation thatmodels the performance of the beam steering unit 430 in FIG. 3 ,according to some embodiments. That is, the beam steering unit 430 maybe configured as a linear phase shifter to steer the optical beams thatpass through the beam steering unit 430. The beam steering unit 430 mayset the angle θ of the optical beam by shifting the phase of an opticalbeam according to the following equations:

$\begin{matrix}{\theta = {\frac{\lambda}{2\pi}A}} & (1)\end{matrix}$

where λ=is the optical beam's wavelength; A=is the slope of the linearspatial phase

E˜e ^(ik) ^(z) ^(z) e ^(ikθx)  (2)

; where E=is the optical field; i=is the notation of the imaginary partof a complex value; k=is the optical wave vector; z=is the coordinatealong the optical beam propagation direction

FIG. 8 is a block diagram illustrating an example structure of a beamsteering unit, according to some embodiments. The beam steering unit 800(e.g., beam steering unit 430 in FIG. 4 ) includes a thin layer of LCthat is sandwiched between two indium tin oxide (ITO) conductive layers.The first layer is coupled to a ground supply and the second layer ispixellated. In some embodiments, the LC layer thickness is on the orderof ten to tens of micrometers. In some embodiments, the ITO is opticallytransparent. In some embodiments, the whole structure is between twoglass substrates that are of several tenth millimeter thick. By applyingdifferent voltages on the ITO pixels, it can form a linear phase delayor retardation across the pixels.

FIG. 9 is a graph illustrating the relationship between control voltageand birefringence phase delay or retardation of a beam steering unit,according to some embodiments. In this embodiment, the beam steeringunit includes a thin LC of several micrometers. The graph 900 shows thatthe higher the voltage is, then the less the optical birefringence phasedelay. To form a linear spatial phase retardation profile across allpixels, the phase retardation at each pixel is calculated with thelinear phase function, and the required voltage for each pixel iscalculated with the retardation vs. voltage curve.

FIG. 10 is a flow diagram illustrating an example method for beamsteering compensation in an FMCW LIDAR system to enhance detection ofdistant objects, according to some embodiments. Additional, fewer, ordifferent operations may be performed in the method depending on theparticular arrangement. In some embodiments, some or all operations ofmethod 1000 may be performed by one or more processors executing on oneor more computing devices, systems, or servers (e.g., remote/networkedservers or local servers). In some embodiments, method 1000 may beperformed by a signal processing unit, such as signal processing unit112 in FIG. 1 . In some embodiments, method 1000 may be performed by anyof the components (e.g., scanner 302, GP 428, beam steering unit 430,voltage control unit 120, etc.) in environment 400 in FIG. 4 , and/orthe components in environment 500 in FIG. 5 . Each operation may bere-ordered, added, removed, or repeated.

In some embodiments, the method 1000 may include the operation 1002 oftransmitting, by an optical scanner, an optical beam towards an objectbased on a transmit optical beam that propagates along an optical axis.In some embodiments, the method 1000 may include the operation 1004 ofreceiving, by a first optical element responsive to transmitting theoptical beam, a returned reflection having a lag angle relative to theoptical axis. In some embodiments, the method 1000 may include theoperation 1006 of steering, by the first optical element, the returnedreflection to generate a first steered beam.

In some embodiments, the method 1000 may include the operation 1008 ofreceiving, by a beam steering unit, the first steered beam and a localoscillator (LO) signal associated with the transmit optical beam,wherein the first steered beam is propagating at a first beam anglerelative to the optical axis and the LO signal is propagating at a firstLO angle relative to the optical axis. In some embodiments, the method1000 may include the operation 1010 of steering, by the beam steeringunit, the first steered beam based on an array voltage to generate asecond steered beam at a first location on a photodetector.

In some embodiments, the method 1000 may include the operation 1012 ofsteering, by the beam steering unit, the LO signal based on the arrayvoltage to generate a steered LO signal at a second location on thephotodetector, wherein a beam offset between the first location and thesecond location is caused by the lag angle. In some embodiments, themethod 1000 may include the operation 1014 of adjusting, by a processor,the array voltage to cause the beam steering unit to reduce the beamoffset between the first location and the second location.

The preceding description sets forth numerous specific details such asexamples of specific systems, components, methods, and so forth, inorder to provide a good understanding of several embodiments of thepresent disclosure. It will be apparent to one skilled in the art,however, that at least some embodiments of the present disclosure may bepracticed without these specific details. In other instances, well-knowncomponents or methods are not described in detail or are presented insimple block diagram format in order to avoid unnecessarily obscuringthe present disclosure. Thus, the specific details set forth are merelyexemplary. While this specification contains many specificimplementation details, these should not be construed as limitations onthe scope of any inventions or of what may be claimed, but rather asdescriptions of features specific to particular embodiments ofparticular inventions. Certain features that are described in thisspecification in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable sub-combination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination can in some casesbe excised from the combination, and the claimed combination may bedirected to a sub-combination or variation of a sub-combination.Moreover, the separation of various system components in the embodimentsdescribed above should not be understood as requiring such separation inall embodiments, and it should be understood that the described programcomponents and systems can generally be integrated together in a singlesoftware product or packaged into multiple software products. Particularembodiments may vary from these exemplary details and still becontemplated to be within the scope of the present disclosure.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiments included inat least one embodiment. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment” in various places throughout thisspecification are not necessarily all referring to the same embodiment.In addition, the term “or” is intended to mean an inclusive “or” ratherthan an exclusive “or.”

Although the operations of the methods herein are shown and described ina particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operations may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be in an intermittent oralternating manner.

The above description of illustrated implementations of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific implementations of, and examples for, the invention aredescribed herein for illustrative purposes, various equivalentmodifications are possible within the scope of the invention, as thoseskilled in the relevant art will recognize. The words “example” or“exemplary” are used herein to mean serving as an example, instance, orillustration. Any aspect or design described herein as “example” or“exemplary” is not necessarily to be construed as preferred oradvantageous over other aspects or designs. Rather, use of the words“example” or “exemplary” is intended to present concepts in a concretefashion. As used in this application, the term “or” is intended to meanan inclusive “or” rather than an exclusive “or”. That is, unlessspecified otherwise, or clear from context, “X includes A or B” isintended to mean any of the natural inclusive permutations. That is, ifX includes A; X includes B; or X includes both A and B, then “X includesA or B” is satisfied under any of the foregoing instances. In addition,the articles “a” and “an” as used in this application and the appendedclaims should generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Moreover, use of the term “an embodiment” or “one embodiment” or“an implementation” or “one implementation” throughout is not intendedto mean the same embodiment or implementation unless described as such.Furthermore, the terms “first,” “second,” “third,” “fourth,” etc. asused herein are meant as labels to distinguish among different elementsand may not necessarily have an ordinal meaning according to theirnumerical designation.

What is claimed is:
 1. A method comprising: transmitting an optical beamtowards an object based on a transmit optical beam that propagates alongan optical axis; receiving, responsive to transmitting the optical beam,a returned reflection having a lag angle relative to the optical axis;directing the returned reflection to generate a first directed beam;receiving the first directed beam and a local oscillator (LO) signalassociated with the transmit optical beam; directing the first directedbeam based on an array voltage to generate a second directed beam at afirst location on an optical element; directing the LO signal based onthe array voltage to generate a directed LO signal at a second locationon the optical element; and adjusting, by a processor, the array voltageto reduce a beam offset between the first location and the secondlocation.
 2. The method of claim 1, wherein at least one of: the firstdirected beam is propagating at a first beam angle relative to theoptical axis, the LO signal is propagating at a first LO angle relativeto the optical axis, the second directed beam propagates at a secondbeam angle relative to the optical axis, or the directed LO signalpropagates at a second LO angle relative to the optical axis.
 3. Themethod of claim 2, wherein the second beam angle of the second directedbeam is generated further based on the first beam angle of the firstdirected beam.
 4. The method of claim 2, wherein the second LO angle ofthe directed LO signal is generated further based on the first LO angleof the LO signal.
 5. The method of claim 2, further comprising:adjusting the first beam angle of the first directed beam and the firstLO angle of the LO signal by an equal amount that corresponds to thearray voltage.
 6. The method of claim 1, further comprising: directing,by a reflective glass plate, the first directed beam to adjust an angleof the first directed beam relative to the optical axis prior toreceiving the first directed beam.
 7. The method of claim 6, furthercomprising: receiving, by a second optical element, the first directedbeam responsive to directing, by the reflective glass plate, the firstdirected beam to adjust the angle of the first directed beam relative tothe optical axis; and directing, by the second optical element, thefirst directed beam to further adjust the angle of the first directedbeam relative to the optical axis.
 8. The method of claim 1, wherein theoptical beam is a frequency-modulated continuous wave (FMCW) opticalbeam.
 9. The method of claim 1, wherein adjusting, by the processor, thearray voltage to reduce the beam offset between the first location andthe second location comprises: applying the array voltage to a patternedelectrode of a liquid crystal-filled plate to cause a linear phaseretardation to form along one direction.
 10. The method of claim 9,wherein the linear phase retardation causes a linear spatial phase on awavefront of the first directed beam.
 11. A light detection and ranging(LIDAR) system comprising: an optical scanner to: transmit an opticalbeam towards an object based on a transmit optical beam that propagatesalong an optical axis; a first optical element to: receive, responsiveto the transmit of the optical beam, a returned reflection having a lagangle relative to the optical axis; direct the returned reflection togenerate a first directed beam; a beam directing unit to: receive thefirst directed beam and a local oscillator (LO) signal associated withthe transmit optical beam; direct, based on a first array voltage, thefirst directed beam to generate a second directed beam at a firstlocation on a different optical element; direct, based on the firstarray voltage, the LO signal to generate a directed LO signal at asecond location on the different optical element; and direct, based on asecond array voltage, the second directed beam to reduce a beam offsetbetween the first location and the second location.
 12. The LIDAR systemof claim 11, wherein at least one of: the first directed beam ispropagating at a first beam angle relative to the optical axis, the LOsignal is propagating at a first LO angle relative to the optical axis,the second directed beam propagates at a second beam angle relative tothe optical axis, or the directed LO signal propagates at a second LOangle relative to the optical axis.
 13. The LIDAR system of claim 12,wherein, the second beam angle of the second directed beam is generatedfurther based on the first beam angle of the first directed beam. 14.The LIDAR system of claim 12, wherein the second LO angle of thedirected LO signal is generated further based on the first LO angle ofthe LO signal.
 15. The LIDAR system of claim 12, wherein the beamdirecting unit to: adjust the first beam angle of the first directedbeam and the first LO angle of the LO signal by an equal amount thatcorresponds to the first array voltage.
 16. The LIDAR system of claim11, further comprising: a reflective glass plate to adjust an angle ofthe first directed beam relative to the optical axis prior to receive,by the beam directing unit, the first directed beam.
 17. The LIDARsystem of claim 16, further comprising: a second optical element to:receive the first directed beam responsive to steer the first directedbeam to adjust the angle of the first directed beam relative to theoptical axis; direct the first directed beam to further adjust the angleof the first directed beam relative to the optical axis; and provide thefirst directed beam to the beam directing unit.
 18. The LIDAR system ofclaim 11, wherein the optical beam is a frequency-modulated continuouswave (FMCW) optical beam.
 19. The LIDAR system of claim 11, wherein thebeam directing unit comprises a liquid crystal-filled plate having apatterned electrode.
 20. A light detection and ranging (LIDAR) systemcomprising: an optical scanner to: transmit an optical beam towards anobject based on a transmit optical beam that propagates along an opticalaxis; a first optical element to: receive, responsive to the transmit ofthe optical beam, a returned reflection having a lag angle relative tothe optical axis; and direct the returned reflection to generate a firstdirected beam; and a beam directing unit to: receive the first directedbeam; direct, based on a first array voltage, the first directed beam togenerate a second directed beam at a first location on a differentoptical element; and direct, based on a second array voltage, the seconddirected beam from the first location on the different optical elementto a second location on the different optical element to compensate forthe lag angle.